QJ23型直流单臂电桥面板上的按钮“G”为（）的开关。
A.检流计支路
B.电源支路
C.比例臂
D.比较臂
参考答案：A
(2013·济南市一模)—I will have to think about it again.
—If you ________， you may lose the opportunity to compete altogether.
A．hesitate
B．wonder
C．continue
D．fail
到两坐标轴距离分别为a，b（a，b为非负常数）的点的个数是______．
